Work by scientists could lead to a non-invasive blood test to detect genetic abnormalities such as Down's syndrome in the womb.

Current non-invasive tests - such as ultrasound - are limited, and invasive tests pose a risk to the pregnancy.

The new technique works by examining samples of foetal DNA present in the mother's blood for tiny variations in the sequence of the genetic material.

US firm Ravgen Inc's work is detailed online by the Lancet.

Experts say other approaches may also bear fruit.

Most people think one of these technologies will eventually be refined enough to be useful in clinical practice

Dr Lyn ChittyUniversity College London Hospital

Being able to identify genetic abnormalities at an early stage not only gives parents the chance to decide whether or not to proceed with the pregnancy, but also alerts medical staff to the need for close monitoring right through to birth.

Analysing foetal DNA from a mother's blood sample has been possible for some time.

However, its effectiveness has been limited because only a small amount of the DNA makes its way into the mother's blood.

Characteristic pattern

The Ravgen team, led by Ravinder Dhallan, has been able to maximise the amount of DNA that can be recovered by treating the blood samples with a chemical called formaldehyde.

The researchers took blood samples from 60 pregnant women.

They then searched the genetic material for variations known as single nucleotide polymorphisms (SNPs).

As each chromosome has a characteristic pattern of SNPs, the researchers were able to distinguish between DNA from the mother and the foetus.

They were also able to determine whether the foetus was carrying extra copies of key chromosomes which cause genetic disease.